How long does Beyfortus (nirsevimab) last?

One dose of Beyfortus (nirsevimab) protects your child from serious RSV for about [5 months](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=2f08fa60-f674-432d-801b-1f9514bd9b39&type=display#section-11.3:~:text=BEYFORTUS%20extends%20through-,5%20months,-.). This should cover the whole [RSV season](https://www.cdc.gov/rsv/about/index.html). Beyfortus (nirsevimab) only provides protection for a relatively short time. So, babies born outside of the RSV season should wait to get the injection when the season starts. Talk to your child's pediatrician about [the best time](https://www.goodrx.com/beyfortus/how-it-works-faqs) for your child to get Beyfortus (nirsevimab).

Can Beyfortus (nirsevimab) be given with other vaccines?

According to the CDC, Beyfortus (nirsevimab) [can be given at the same time as other routine childhood vaccines](https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/infants-young-children.html#:~:text=Coadministration%20with%20vaccines). They can be given during the same visit. There isn't a lot of information, but Beyfortus (nirsevimab) isn't expected to cause problems with other vaccines. Talk to your child's pediatrician if you have any questions.

Is Beyfortus (nirsevimab) an mRNA vaccine?

No. Beyfortus (nirsevimab) isn't an [mRNA vaccine](https://www.goodrx.com/conditions/covid-19/mrna). Beyfortus (nirsevimab) is an injection that provides your body with lab-made antibodies. mRNA vaccines work by teaching your cells to make proteins that then cause your immune system to make [antibodies](https://www.genome.gov/genetics-glossary/Antibody). These antibodies fight off germs and viruses if they get into your body later in the future. Beyfortus (nirsevimab) works in a different way. It gives you ready-made antibodies to help protect against RSV.

How effective is Beyfortus (nirsevimab)?

Clinical studies and real-world results show that Beyfortus (nirsevimab) works very well for babies and young children. It can [lower the risk](https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/infants-young-children.html) of needing to go to the hospital for RSV by 80% to 90%. It also reduces the chance of getting a serious RSV lung infection that needs medical care by about 80%.

Where do you get Beyfortus (nirsevimab)?

Your child can get Beyfortus (nirsevimab) at a few places. This includes [pediatrician offices, hospitals, and public health clinics](https://www.goodrx.com/beyfortus/how-to-prevent-rsv-in-babies). Ask a healthcare professional to find out where your child can get Beyfortus (nirsevimab).

How long does Beyfortus (nirsevimab) take to work?

Beyfortus (nirsevimab) starts working [within hours](https://www.goodrx.com/beyfortus/how-it-works-faqs) after your child gets the injection. In studies, it reached its highest level in the blood in about 6 days. Beyfortus (nirsevimab) works fast because it's a monoclonal antibody, not a traditional vaccine. It gives your baby read-made antibodies to protect against RSV right away. Vaccines are different – it takes more time for your body to use your immune system to make its own antibodies.

What's the difference between Synagis and Beyfortus?

Beyfortus (nirsevimab) and [Synagis (palivizumab)](https://www.goodrx.com/synagis/what-is) are both injections that help protect babies and infants from getting very sick from [RSV](https://www.goodrx.com/conditions/childhood-rsv). But they're used in [different situations](https://www.goodrx.com/conditions/childhood-rsv/beyfortus-vs-synagis). Beyfortus is for all newborns and infants during their first RSV season. It can also be given to children up to 24 months old for their second RSV season if they're at high risk. Synagis is only approved for babies who were born [premature](https://www.goodrx.com/conditions/pregnancy/bringing-home-your-preemie) (early) and are 6 months or younger when RSV season starts. It's also for children up to 24 months old who have certain health problems. How often the injection is given into the muscle is also different for each medication. Beyfortus (nirsevimab) is given just once at the start of the RSV season. But Synagis is given every month during the season. Talk to a pediatrician to [compare](https://www.goodrx.com/compare/beyfortus-vs-synagis) the two medication and see which one is right for your child.

Beyfortus

nirsevimab

Used for RSV

Beyfortus (nirsevimab or nirsevimab-alip) is an injection given to babies and children up to 24 months old. It's used to prevent them from getting very sick from respiratory syncytial virus (RSV). It's not an RSV vaccine. Instead, it's a monoclonal antibody that gives protection against the virus for a short time. Beyfortus (nirsevimab) is now part of the CDC Child Immunization Schedule. The usual dosage is 1 to 2 injections into the muscle during or at the start of the RSV season. It's well-tolerated with only a few side effects.

Reviewed by:

Kristianne Hannemann, PharmD

Cydnee Ng, PharmD

Last reviewed on August 11, 2025

What is Beyfortus (nirsevimab)?

What is Beyfortus (nirsevimab) used for?

Prevention of respiratory syncytial virus (RSV) in young children of certain ages
- Newborns and infants born during or entering their first RSV season
- Children up to 24 months old at risk of severe RSV illness through their second RSV season

How Beyfortus (nirsevimab) works

Beyfortus (nirsevimab) is a type of monoclonal antibody. It attaches to a specific protein found on RSV (called the prefusion F protein).

By attaching to this protein, it prevents RSV from getting into cells and spreading in the body. This helps protect against RSV and lower the risk of serious illness if you do get sick from it.

When does Beyfortus (nirsevimab) start working?Time passed since treatment started:

HOURS

Full effect

DAYS

WEEKS

MONTHS

Drug facts

Common BrandsBeyfortus

Drug ClassMonoclonal antibody

Controlled Substance ClassificationNot a controlled medication

Generic StatusNo lower-cost generic available

AvailabilityPrescription only

More on Beyfortus (nirsevimab) essentials

Baby at medical checkup.
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RSV Prevention in Babies: Who’s Eligible for Beyfortus and How to Access It

Written by Kristianne Hannemann, PharmD

A mother brings her infant child to a medical appointment.
SDI Productions/E+ via Getty Images

Beyfortus vs. Synagis for RSV Prevention in Children: 6 Differences Parents Should Know

Written by Alyssa Billingsley, PharmD

Side effects of Beyfortus (nirsevimab)

The following side effects may get better over time as your body gets used to the medication. Let your healthcare provider know immediately if you continue to experience these symptoms or if they worsen over time.

Common Side Effects

Side effects aren't common. See Other Side Effects.

Less Common Side Effects

Rash
Injection site reaction (e.g., pain, hard lump, swelling)

Beyfortus (nirsevimab) serious side effects

Contact your healthcare provider immediately if you experience any of the following.

Severe allergic reaction: rash, trouble breathing, swelling in the face or throat

When do Beyfortus (nirsevimab) possible side effects begin and end?

Time passed since treatment started:

HHOURS

DDAYS

WWEEKS

MMONTHS

Rash

Injection site reaction

Source: DailyMed

The following Beyfortus (nirsevimab) side effects have also been reported

Side effects that you should report to your care team as soon as possible:

Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat

Side effects that usually do not require medical attention (report these to your care team if they continue or are bothersome):

Pain, redness, or irritation at injection site
Skin rash

Pros and cons of Beyfortus (nirsevimab)

Pros

Given during one medical visit
Can lower the risk of severe RSV-related illness by about 70% in full-term and premature babies
Not many side effects

Cons

Injection can be uncomfortable
Protection might only last for about 5 months
Not known if it's safe or if it works well for children older than 24 months

Pharmacist tips for Beyfortus (nirsevimab)

Your child should get Beyfortus (nirsevimab) at the start of or during the RSV season. It's usually between late fall and early spring. Ask your child's pediatrician about when RSV season begins in your area. This can help you plan out when your child should get the injection.
Your child could get a rash after getting Beyfortus (nirsevimab). There could also be pain and swelling where the injection was given. These side effects usually happen within 1 to 2 weeks of the injection. But they should go away in a few days. Talk to a healthcare professional about ways to help relieve these side effects.
If your child got Beyfortus (nirsevimab) for their first RSV season, ask the pediatrician if they should get it again for the next season. This usually depends on if your child is still at high risk of getting very sick from RSV.
Even though Beyfortus (nirsevimab) can lower your child's risk of RSV, they could still get infected and get sick. Watch out for symptoms of RSV. They include a stuffy or runny nose, cough, sore throat, and a low-grade fever.
If your child has heart surgery, talk to the pediatrician. Your child might need an extra dose of Beyfortus (nirsevimab) afterwards. Heart surgery might affect the levels of the antibody medication in the body. So an extra dose helps make sure your child is still protected enough from RSV.

More on Beyfortus (nirsevimab) tips

New parents holding their newborn
FatCamera/E+ via Getty Images

RSV Prevention in Children: Your GoodRx Guide to Abrysvo vs. Beyfortus

Written by Amy B. Gragnolati, PharmD, BCPS

Common questions about Beyfortus

One dose of Beyfortus protects your child from serious RSV for about 5 months. This should cover the whole RSV season. Beyfortus only provides protection for a relatively short time. So, babies born outside of the RSV season should wait to get the injection when the season starts. Talk to your child's pediatrician about the best time for your child to get Beyfortus.

Beyfortus is usually safe for protecting infants and young children from serious RSV lung infections. Some kids can have side effects like injection site reactions and rash. Although rare, there's a risk of more serious allergic reactions. If you're worried about how safe Beyfortus is, talk to your child's pediatrician. They can help explain the risks and benefits of the medication.

According to the CDC, Beyfortus can be given at the same time as other routine childhood vaccines. They can be given during the same visit. There isn't a lot of information, but Beyfortus isn't expected to cause problems with other vaccines. Talk to your child's pediatrician if you have any questions.

No. Beyfortus isn't an mRNA vaccine. Beyfortus is an injection that provides your body with lab-made antibodies. mRNA vaccines work by teaching your cells to make proteins that then cause your immune system to make antibodies. These antibodies fight off germs and viruses if they get into your body later in the future. Beyfortus works in a different way. It gives you ready-made antibodies to help protect against RSV.

Clinical studies and real-world results show that Beyfortus works very well for babies and young children. It can lower the risk of needing to go to the hospital for RSV by 80% to 90%. It also reduces the chance of getting a serious RSV lung infection that needs medical care by about 80%.

Your child can get Beyfortus at a few places. This includes pediatrician offices, hospitals, and public health clinics. Ask a healthcare professional to find out where your child can get Beyfortus.

Beyfortus starts working within hours after your child gets the injection. In studies, it reached its highest level in the blood in about 6 days. Beyfortus works fast because it's a monoclonal antibody, not a traditional vaccine. It gives your baby read-made antibodies to protect against RSV right away. Vaccines are different – it takes more time for your body to use your immune system to make its own antibodies.

Beyfortus and Synagis (palivizumab) are both injections that help protect babies and infants from getting very sick from RSV. But they're used in different situations. Beyfortus is for all newborns and infants during their first RSV season. It can also be given to children up to 24 months old for their second RSV season if they're at high risk. Synagis is only approved for babies who were born premature (early) and are 6 months or younger when RSV season starts. It's also for children up to 24 months old who have certain health problems. How often the injection is given into the muscle is also different for each medication. Beyfortus is given just once at the start of the RSV season. But Synagis is given every month during the season. Talk to a pediatrician to compare the two medication and see which one is right for your child.

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Risks and warnings for Beyfortus (nirsevimab)

Beyfortus (nirsevimab) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.

Severe allergic reaction

Some children have had serious allergic reactions after getting Beyfortus (nirsevimab). These reactions can include hives, trouble breathing, or weak muscles. Anaphylaxis has also happened with other monoclonal antibody medications. This can be life-threatening.

If your child has trouble breathing, a severe rash, or swelling in their face, get medical help right away.

Caution use in children with bleeding problems

Risk factors: History of bleeding problems | History of low platelets | Taking blood-thinning medication

Tell your child's healthcare professional about if they have a history of bleeding problems, like low platelets. Also make sure to give them a list of your child's current medications. They can check if your child is taking any blood-thinning medications.

If this is the case, your child might still be able to receive Beyfortus (nirsevimab). But their healthcare team will want to keep an eye on them for any bleeding after the injection.

Beyfortus (nirsevimab) dosage

Typical dosage for Beyfortus (nirsevimab)

Beyfortus (nirsevimab) is injected into the front side of the thigh muscle. It's injected by a trained healthcare professional.

Newborns and infants born during or entering their first RSV season
- Weigh less than 5 kg (11 lbs): The typical dose is 50 mg given as one injection.
- Weigh 5 kg (11 lbs) or more: The typical dose is 100 mg given as one injection.
Children up to 24 months old at risk of severe RSV illness in their second RSV season
- The typical dose is 200 mg, given as two 100 mg injections during one office visit.

Note: Children who need heart surgery might need an extra dose of Beyfortus (nirsevimab) afterwards.

What are alternatives to Beyfortus (nirsevimab)?

There are a number of medications that your doctor can prescribe in place of Beyfortus (nirsevimab). Compare a few possible alternatives below.

Beyfortus (nirsevimab)

Used for:

Prevention of respiratory syncytial virus (RSV) in young children of certain ages
- Newborns and infants born during or entering their first RSV season
- Children up to 24 months old at risk of severe RSV illness through their second RSV season

View prices

Synagis (palivizumab)

Used for:

Prevention of serious respiratory syncytial virus (RSV) infections for:

Babies born premature and are 6 months or younger at the start of RSV season
Children diagnosed with bronchopulmonary dysplasia (BPD) within the last 6 months, and are 2 years or younger at the start of RSV season
Children with congenital heart disease (CHD) and are 2 years or younger at the start of RSV season

View prices

News about Beyfortus (nirsevimab)

RSV Prevention in Children: Your GoodRx Guide to Abrysvo vs. Beyfortus

Compare the differences between Abrysvo, an RSV vaccine for adults, and Beyfortus, a preventative antibody injection for children. Read on to learn more.

Beyfortus vs. Synagis for RSV Prevention in Children: 6 Differences Parents Should Know

Beyfortus and Synagis are two injections that can prevent RSV in children. They are not vaccines. Here are the main differences in eligibility, availability, and more.

How Much Does the RSV Vaccine Cost?

The RSV vaccine for adults can cost about $350 without insurance. But it is covered by many insurance plans, including Medicare. Find out prices and ways to save.

RSV Prevention in Babies: Who’s Eligible for Beyfortus and How to Access It

Beyfortus is one of a few methods that help prevent RSV in children. Learn more about how to prevent RSV in babies with this guide.

How Does Beyfortus Work? Plus, 6 Other Beyfortus FAQs Answered

Beyfortus is a preventive RSV medication that works by providing antibodies. Learn when to get Beyfortus, how long it takes to work, and more.

Beyfortus (nirsevimab) images

This medicine is Yellow Carton.yellow - Beyfortus 100mg/mL Solution for Injection

References

Best studies we found

Centers for Disease Control and Prevention. (2023). Respiratory syncytial virus (RSV) preventive antibody: Immunization information statement (IIS).

Centers for Disease Control and Prevention. (2025). Child immunization schedule notes.

Sanofi Pasteur Inc. (2024). Beyfortus- nirsevimab injection [package insert]. DailyMed.

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

Common questions about Beyfortus

Your child can get Beyfortus at a few places. This includes pediatrician offices, hospitals, and public health clinics. Ask a healthcare professional to find out where your child can get Beyfortus.

Beyfortus